Note 19 - Statutory Information Statutory Information (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) years state	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Statutory Accounting Practices [Line Items]
Risk To Capital Ratio, Regulatory Maximum		25
Restricted Net Assets Held by Consolidated Subsidiaries		$ 3,600,000
Differences Between GAAP Basis and STAT Basis [Member]
STAT Accounting Information [Abstract]
Mortgage Guaranty Insurance Companies Are Required Each Year To Establish A Contingency Reserve Equal To This Percentage Of Premiums Earned In Such Year		50.00%
Number Of Years A Fifty Percent Contingency Reserve Is Required To Be Maintained | years		10
Mortgage Guaranty Insurance Companies Contingency Reserve May Be Reduced With Regulatory Approval To The Extent That Losses In Any Calendar Year Exceed This Percentage Of Earned Premiums For Such Year		35.00%
PENNSYLVANIA
Statutory Accounting Practices [Line Items]
Policyholder Dividends, Rate on Policy Earnings		10.00%
State Insurance Regulations [Member]
Statutory Accounting Practices [Line Items]
Number Of States That Have A Statutory Or Regulatory Risk Based Capital Requirement | state		16
Minimum [Member] | Non RBC States [Member]
STAT Accounting Information [Abstract]
Capital Required for Capital Adequacy		$ 1,000
Maximum [Member] | Non RBC States [Member]
STAT Accounting Information [Abstract]
Capital Required for Capital Adequacy		5,000
Radian Reinsurance [Member]
Statutory Accounting Practices [Line Items]
Investments in and Advances to Affiliates, at Fair Value, Period Increase (Decrease)		175,000		$ 266,000
Statutory Accounting Practices, Statutory Policyholders' Surplus, Balance		328,900	$ 147,600	138,700
Statutory Unassigned Negative Surplus		112,100	118,400
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments		0
STAT Accounting Information [Abstract]
Statutory Accounting Practices, Statutory Capital and Surplus, Increase (Decrease)	$ (175,000)
Capital Contributions	175,000
Radian Guaranty [Member]
Statutory Accounting Practices [Line Items]
Investments in and Advances to Affiliates, at Fair Value, Period Increase (Decrease)		100,000
Statutory Accounting Practices, Statutory Policyholders' Surplus, Balance		1,201,000	1,349,700	1,686,500
Surplus Notes		100,000	0	325,000
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments		0
STAT Accounting Information [Abstract]
Statutory Accounting Practices, Dividends Paid with Approval of Regulatory Agency	175,000
Statutory Accounting Practices, Statutory Capital and Surplus, Increase (Decrease)	$ (175,000)
Cumulative Earnings (Deficit)		765,000	691,300
Other MI Companies [Member]
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Statutory Policyholders' Surplus, Balance		58,600	57,100	55,000
Parent Company [Member]
Statutory Accounting Practices [Line Items]
Investments in and Advances to Affiliates, at Fair Value, Period Increase (Decrease)		521,000	2,500	$ 398,300
Restricted Net Assets Held by Consolidated Subsidiaries		$ 3,764,865	$ 3,383,089
STAT Accounting Information [Abstract]
Related Party Transaction, Rate		0.00%		0.00%
Parent Company [Member] | Minimum [Member]
STAT Accounting Information [Abstract]
Surplus Note, Notice of Redemption Period		30 days